Phylum MolluskaPhylum Molluska•Over 50,000 speciesOver 50,000 species•CoelomateCoelomate, , ProtostomesProtostomes, Bilaterally , Bilaterally symmetricalsymmetrical•Mostly marine, although some live in Mostly marine, although some live in fresh water or land.fresh water or land.•Generally soft-bodied with a hard shellGenerally soft-bodied with a hard shell•However, squid & octopi have However, squid & octopi have internalized, reduced or lost their internalized, reduced or lost their shells.shells.•Body PlanBody Plan•Although phenotypically diverse, Although phenotypically diverse, mollusks share 3 common featuresmollusks share 3 common features•A muscular footA muscular foot - usually for movement - usually for movement•A visceral massA visceral mass - including internal - including internal organsorgans•A A mantlemantle - envelopes visceral mass and - envelopes visceral mass and secretes a shellsecretes a shell

Molusk General AnatomyMolusk General Anatomy

Class Polyplacophora Class Polyplacophora (chitons)(chitons)

• Marine animals - shells divided into 8 platesMarine animals - shells divided into 8 plates• Move using a muscular foot and graze using a Move using a muscular foot and graze using a

scraping mouthpart called a scraping mouthpart called a radularadula

Chiton AnatomyChiton Anatomy

ChitonsChitons

Class BivalviaClass Bivalvia• Include clams, oysters Include clams, oysters

and musselsand mussels• Have shells divided Have shells divided

into 2 halves, into 2 halves, connected by strong connected by strong musclesmuscles

• Has hatchet shaped Has hatchet shaped foot for digging and foot for digging and anchoringanchoring

• Are typically filter Are typically filter feeders drawing in feeders drawing in water end expelling it water end expelling it through a siphon tubethrough a siphon tube

• Generally sessile, Generally sessile, however, some species however, some species can quickly move by can quickly move by rapidly closing it's rapidly closing it's shellshell

Bivalve Anatomy

BivalvesBivalves

Class GastropodaClass Gastropoda• Include snails, Include snails,

abalone, and slugsabalone, and slugs• Largest class of Largest class of

mollusks ~40,000 mollusks ~40,000 speciesspecies

• Exhibit embryonic Exhibit embryonic process of process of torsiontorsion

• Visceral mass twists Visceral mass twists 18018000 during development during development

• Most species are Most species are herbivores, but some herbivores, but some have modified have modified radullasradullas for boring into other for boring into other mollusksmollusks

• Some species have Some species have successfully colonized successfully colonized land land

Gastropods

Giant African Land SnailGiant African Land Snail

Class CephalopodaClass Cephalopoda• Unlike other mollusks, Unlike other mollusks,

these are quick predatorsthese are quick predators• Have beak-like jaws and Have beak-like jaws and

poison to catch & poison to catch & immobilize preyimmobilize prey

• Beak is located @ the Beak is located @ the center of several long center of several long tentaclestentacles

• Foot has been modified to Foot has been modified to form a form a siphonsiphon which allows which allows most species to move most species to move quickly using a jet of quickly using a jet of water.water.

• Only mollusks with a Only mollusks with a closed closed circulatory systemcirculatory system (blood (blood is always contained in is always contained in vessels)vessels)

• Very highly developed Very highly developed nervous systemnervous system

• Can learn complex behaviorsCan learn complex behaviors• Octopi have learned to open Octopi have learned to open

jars to retrieve preyjars to retrieve prey• May have rudimentary May have rudimentary

communicationcommunication• Cuttlefish and octopi may Cuttlefish and octopi may

communicate by skin communicate by skin coloration coloration

Cephalopod AnatomyCephalopod Anatomy

OctopusOctopus

SquidSquid

CuttlefishCuttlefish

Cambered NautilusCambered Nautilus